New synthetic methods using the TiCl4-NR3 reagent system

Issue in Honor of Prof. S. V. Kessar ARKIVOC 2002 (vii) 151-166 Ph HO COOMe Ph COOMe TiCl4/Pyridine Ph + HO CHCOOMe COOMe THF, 25 0C O HO Ph 21% 77 % Scheme 33 The TiCl4/Et3N combination oxidizes dihydrobenzoin and benzoin to benzil (Scheme 34).31 Ph Ph HO O TiCl4/Et3N CH2Cl2 HOPh OPh 77% Ph O Ph TiCl4/Et3N O CH2Cl2 HO Ph O Ph 48% Scheme 34 Propargyl alcohols are oxidized to the corresponding aldehydes under similar conditions (Scheme 35).32 R = n-C12H25 90% R = Ph3Si 98% R= HO(CH2)2-CH2 89% Scheme 35 As discussed previously (Scheme 25), the TiCl3 species are produced in the reaction of TiCl4 with NR3. We have observed that the TiCl3 produced in situ in this way can be readily exploited to achieve reductive coupling of aromatic aldehydes and aldimines (Scheme 36).33 OH R O R H TiCl4/NEt3 ISSN 1424-6376 Page 163 ©ARKAT USA, Inc